In order to produce a high power cylindrical electrochemical cell with low electrical impedance, current production techniques require multiple electrically conducting tabs to be attached, normally by welding, to the electrode substrate foil at several points along the electrode length. In order to decrease the cell impedance, the number of tabs are increased accordingly.
Several conventional methods of discrete tab attachment are currently employed in the manufacture of electrochemical storage cells, electrochemical capacitors, electrolytic capacitors, dry film capacitors and similar electrical devices. Conventional methods for discrete tab attachment include removing a coating in regions on both sides of a coated electrode and welding tabs to the exposed uncoated regions, and subsequently applying an insulating cover layer over the welded tab and the exposed foil on the opposite side of the electrode from the tab. In other conventional methods, the coating removal step may be avoided by partially coating the electrode surfaces, leaving uncoated coating-free electrode edge foils. Furthermore, tabs may be adhered to or alternately, cut out and formed from uncoated electrode regions. Insulating tape may then be applied to cover the tabs in order to prevent electrical shorting at the tab edges. Conventional methods for providing electrical connection of the electrodes to the wound electrode assembly without discrete tabs include blind through welding of coating-free edge foils to a plate. Electrical connection may also be provided by holding a plate in mechanical compression against the uncoated electrode foil edges.
The inventors herein have recognized potential issues with the above approaches. Namely, with the use of discrete tabs, electrical current may be channeled to a small area of the tabs at discrete points along the electrode, creating areas that may operate at significantly higher temperature than the remainder of the electrode due to high localized ohmic heating. Furthermore, cell amp-hour (Ah) capacity is reduced overall due to the uncoated regions for tab attachment, localized differences in the anode to cathode capacity ratio in the uncoated regions may cause localized lithium plating in the case of the Li-ion battery cell chemistry. Further still, cell manufacturing complexity is increased and manufacturing speed is decreased, requiring additional functions to accomplish the coating removal, tab welding and taping operations, and demands a greater financial investment to start up production. In the case of blind through welding at the foil edges, deposition of loose metal particles liberated during welding process into sensitive areas of the wound electrochemical storage cell (e.g., “jellyroll”) assembly may increase production yield loss, and may create electrical shorts during cell use. It may also be difficult to inspect and verify the quality of the welds after they are formed. In the case of mechanical compression, electrical connection may degrade due to oxidation or passivation of the interface surfaces over time, loss of contact force due to shock and vibration, thermal expansion, and component distortion from internal pressures. Furthermore, the contact compressive force required to maintain adequate contact resistance may locally exceed the yield strength of the foils, limiting the power capability of the connection.
One approach that at least partially addresses the above issues includes an electrochemical storage cell, comprising first and second electrode sheets wound around a cylindrical core forming a jellyroll structure, the first and second electrode sheets each comprising uncoated conductive edges parallel to end faces of the jellyroll structure, and coated opposing surfaces between the uncoated conductive edges, first and second separator sheets mechanically and electrically separating the coated opposing surfaces of the first and second electrode sheets and mechanically and electrically separating the cylindrical core and the coated opposing surfaces of the first electrode sheet, and slotted cutouts from the uncoated conductive edges, the slotted cutouts angularly co-located relative to the cylindrical core upon forming the jellyroll structure.
In another embodiment, a method for an electrochemical storage cell comprises winding first and second electrode sheets around a cylindrical core to form a jellyroll structure, the first and second electrode sheets each comprising uncoated conductive edges parallel to end faces of the jellyroll structure, and coated opposing surfaces between the uncoated conductive edges, winding first and second separator sheets around the cylindrical core between the first and second electrode sheets to mechanically and electrically separate the coated opposing surfaces of the first and second electrode sheets and to mechanically and electrically separate the cylindrical core and the coated opposing surfaces, and cutting out slots from the uncoated conductive edges of the first and second electrode sheets to form slotted cutouts, the slotted cutouts angularly co-located relative to the cylindrical core upon forming the jellyroll structure.
In another embodiment a method for a cylindrical electrochemical cell comprises forming a first and second electrode, mounting the first and second electrodes on a cylindrical core, winding the first and second electrodes on the cylindrical core, and consolidating the first and second electrodes to electrically connect the first and second electrodes to first and second terminals of the electrochemical storage cell.
It will be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.